1. Field of the Invention
This invention relates to video signal recorder/player devices which are operable to produce video signals (with or without accompanying audio signals) from recorded information, and which are further operable to modulate a carrier signal with these video/audio signals for transporting them to a television receiver in an information channel which is provided in a suitable transmission medium, the information channel having a given bandwidth with respect to the frequency of the carrier signal.
2. Description of Related Art
In the case of a domestic video tape recorder/player device, for which the information channel is commonly known as a "playback channel" and will be so termed hereinafter, the recorder part is tunable selectively to any one of a plurality of UHF television channels to receive and to record onto tape television transmissions transported in these channels.
The UHF television channel allocation for Bands IV and V in the United Kingdom covers 44 channels which are numbered 21 to 34 and 39 to 68, the carrier frequency for adjacent channels being 8 MHz apart. Details of this channel allocation is given in IBA Technical Review No. 10, May 1978, and therefore will not be considered further in the present specification. A similar though possibly extended frequency allocation is used for these bands in Continental Europe.
The playback channel used for a domestic video tape recorder/player device is notionally a particular one of these 44 UHF television channels which has not been allocated to a terrestrial broadcast television station. However, there is often interference present in the playback channel from a broadcast channel transporting a television transmission, depending on where the device is located. There is a facility on many video tape recorder/player devices for making a manual adjustment to the frequency of the carrier signal which defines the playback channel to move the channel relative to an interfering broadcast channel, but this is not always successful in reducing the interference. The interference from broadcast channels has been found to be particularly bad in certain European locations where television transmissions from several different transmitters can be received.
It is known from Japanese Applications Nos. 53-81786 and 59-263429 to provide a video tape recorder in which available television channels are tested for detecting the presence or absence of television transmissions and to use a vacant channel which is found as the playback channel for the video tape recorder. However, as will be considered later in the specification, this relatively simple method of selecting a playback channel has only a limited success in overcoming inter-channel interference in the various transmission and reception requirements which are imposed on present day domestic video tape recorder/player devices.